Furnace for heating pieces by means of high frequency currents



L. DREYFUS Oct. 17, 1939.

FURNACE FOR HEATING PIECES BY MEANS OF HIGH FREQUENCY CURRENTS Filed Dec. 18, 1936 if? ven f0 7 Patented Get. 17, 1939 PATENT OFFICE summon FOR HEATING rlncnsnr MEANS or men FREQUENCY cummnrs Ludwig Dreyfus, Vasteras, Sweden, assignor to Allminna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application December 18, 1936, Serial No. 116,603 In Sweden December 18, 1935 2 Claims (Cl. 219-13) While high frequency currents for melting'and treating metals in a molten state have formed the subject of considerable development work,,means for heating solid metal objects by high-frequency 5 currents without melting, generally speaking, have retained the primitive configuration which they obtained originally, consisting simply of a coil surrounding the more or less cylindrical object. Such an arrangement has, however, in most l cases been found unsuitable ior'the heating of tools, which generally present the characteristic feature that a very limited portion of the metal body, for instance a cutting, abrading or crushing edge, a plane or particularly shaped surface for upsetting, swaging, drop forging or stamping a working piece shall be separately heat treated, for instance for hardening or reforglng, while the rest of the tool should for several reasons maintain a low temperature. In such cases, it is of 20 great importance that the high frequency magnetic field and thereby the eddy currents in the heat treated object are concentrated to the portion thereof, which shall be treated.

The present invention relates to a. means for 25 local heating of tools or the like for the purpose of forming or hardening or for other purposes. In accordance with this invention the portion of the tool or the like (hereinafter referred to as the work piece) to be heated, is introduced into an 0 electric high frequency furnace having a laminated iron shell, through an opening in the said iron shell, said opening being preferably so arranged with respect to the high frequency winding of the furnace and fitting so closely against the working piece, at least in the plane of the laminations, that the alternating flux penetrating the latter will be essentially limited to the portion of the said work piece introduced into the furnace.

A number of difierent forms of furnaces are linked with the bottom bundle l and which ex tend so far inwards as to leave, after the mount-= 55 log of asuitahle protective and heat insulating layer 6, an appropriate space for introducing the drill bit. The coil and the ridge! are protected by another heat insulating layer T against which the drill is held when introduced into the furnace. The right hand half of the Fig, in which the heat 5 insulating layer 1 is omitted, shows instead of that the lines of force penetrating through the drill body 8, said lines of force being, thanks to; the ridge 2 and the shelf-like proiectionsi, concentrated almost exclusivelyto the drill bit. An appropriate heating is thus obtained only here, that is, on a length of 1 to 2 cm. The coil is connected, as an example, to a rotating highfrequency generator it in parallel to a condenser battery l2.

If the drill is to be heated for reforging instead of only for hardening, the shell can be made with a somewhat deeper recess.

Figs. 2 and 3 show two different modifications of the furnace shown in Fig. l. with respect to the configuration of the shell and of the coil. In these figures, only the electrically and magnetically active parts and thelines of force areshown, while all heat insulation and other accessories are omitted. The ridge [3 (Fig. 2). and M (Fig. 3)

are both higher in proportion than in Fig. 1, sothat for the same winding space a still stronger concentration of the flux to the end of the work piece introduced from above is obtained. In Fig. 2, the coil [5 has a constant width, while in Fig. 3 the coil [6 is tapered downwards as in Fig. l. The first form facilitates the winding work, but causes under otherwise equal circumstances a stronger lateral flux.

In all the forms illustrated, the winding is composed of a tubular conductor through which a cooling liquid is led. This is the easiest way to accomplish the necessary cooling. v

The flux diagrams are all drawn without respect to the modifications, which are caused by the currents induced in the work piece or by the generally form-magnetic character of the latter at low temperature. This character generally increases the flux concentration, while at higher temperatures the ohmic resistance generally becomes so high that the eddy currents do not materially modify the character of the flux diagram.

I claim as my invention:

1. Means for heating the ends of bar-shaped work pieces comprising a magnetic shell in the shape of'a prismatic box open along one longitudinal side and having laminations perpendic- -ular to its longitudinal direction, said box having laterally projecting ridges limiting the opening on the open side as compared with the width of the inner space and an upwardly tapering central ridge at the bottom terminating inside said lateral projections, a winding inside said box spaced from the narrower portionof said central ridge and from the most projecting portions of said laterally projecting ridges, and a source oi lar to its longitudinal direction, said box having laterally projecting ledges limiting the opening on the open side ascompared with the width 01' the inner space and an upwardly tapering central ridge at the bottom terminating inside said ledges, a winding inside said box spaced from the narrower portion oi said ridge and from the most projecting portions of said ledges and having an axial length considerably greater than the minimum distance between said ridge and said ledges,

and a source of high frequency current feeding 10 said winding.

' LUDWIG DREYFUS. 

